The present invention relates to an air cannon for removal of cakes of flowable material and clearing clogged areas of flowable material in silos, heat exchangers, lines etc. with the aid of air blasts. The air cannon has a pressure container for storage of compressed air, an outlet jet as well as an outlet valve arranged between the pressure container and the outlet jet for ejecting the compressed air, whereby the outlet valve comprises a valve housing as well as a piston that is axially slidably guided in a guide and is exposed with its rearward to a suddenly releasable closure pressure. The piston has at its forward end that is facing the outlet jet an annular valve sealing surface. The pressure present at the outlet jet acts on an area enclosed by the annular valve sealing surface, and the pressure present within the pressure container acts on an area surrounding the annular valve sealing surface.
Air cannons are devices for generating impulse-type air blasts of high energy density. These air blasts are used to remove caked flowable material or to clear clogged areas of flowable material within silos, heat exchangers, lines of processing plants, cyclones, oven inlets, etc. in periodic time intervals or whenever needed. For this purpose, compressed air within a pressure container is suddenly released via an outlet valve with a great outlet cross-section and expanded. The thus released pressure energy loosens the caked flowable material in the aforementioned devices.
The dimensions as well as the design of the outlet valve employed are very important for the magnitude of the air blast impulse to be generated with such air cannons. From European patent 0 134 726 an air cannon is known in which the outlet valve is a component in which the inlet line coming from the pressurized container is arranged perpendicularly to the outlet jet. This arrangement results in considerable flow and throttle losses for the air exiting through the open outlet valve. Similar disadvantages are also present for the embodiment and guiding of the valve body which is essentially designed as a valve plate with an outer collar and an inner collar. With the inner collar the valve plate rests in its closing position on an annular valve seat of the outlet jet, while the outer collar serves for guiding the valve plate within the valve housing. This known outlet valve forces the air to flow such that first the air is deflected by 90.degree. and subsequently, when entering the outlet jet, is again deflected by 180.degree..
Another air cannon is known from German patent 36 02 207 in which the valve seat is formed by the end of the outlet tube whereby this end of the tube is arranged at the level of the central axis of the inlet line coming from the pressure container. In this manner, a great portion of the pressurized air existing through the open outlet valve is open is only deflected once by 90.degree.. However, since in this construction the outlet tube also partially extends into the inlet line, undesirable flow and pressure losses occur in the area of the collar-shaped valve seat.
Another air cannon is known from the brochure titled "Luftsto.beta.gerate: Sicherer Betrieb und zuverlassige Funktion" of Agrichema Materialflu.beta.technik GmbH. This device has an outlet valve, which is arranged within the pressure container, and an annular valve sealing surface whereby the compressed air flows radially onto the valve sealing surface so that in this case also a deflection of the flow about 90.degree. results. However, in this case the required collar of the outlet tube known from the aforementioned construction is eliminated. Disadvantageously, the outflow with this known outlet valve does not occur uniformly over the entire valve cross-section: Over the circumference of the valve sealing surface a plurality of outlet openings with interposed stays are provided. The stays are extensions of the valve housing of the outlet valve and connect the valve housing with the valve seat. These stays are very unfavorable with respect to flow dynamics because they present a surface perpendicular to the flow direction causing a considerable pressure loss and thus a weakening of the producible air impulse. Furthermore, the arrangement of the outlet valve within the pressure container is disadvantageous with respect to control and servicing of the device. In this context it is important to realize that such pressure containers are subject to the respective pressure container regulations and ordinances and therefore cannot be opened at will.
It is therefore an object of the present invention to provide an air cannon for removal of caked flowable material and clearing of clogged areas of flowable material which is simple in its construction and which generates an especially strong air impulse or air blast.